Good Fruit Grower

March 15

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Enhanced
Biocontrol
CODLING MOTH:
It's what's for dinner.
Sterilized carabid beetle before gut dissection.
Investigating the predators down under
using DNA gut content analysis.
by Angela Gadino, Tom Unruh and Jay Brunner
D
o you ever wonder what those earwigs, spiders,
and other ground-dwelling predators eat in your
orchard?
This question has been a main focus in the
Enhancing Biological Control in Western Orchards
Specialty Crop Research Initiative project. We know these
predators are in our orchards, but up until now who is eating
what has not been well documented, especially with regards
to codling moth.
We set out to look at which major predator groups found
commonly in western orchards might be eating the most
codling moth larvae.
Codling moth larvae, once fully grown inside apples or
pears, leave the fruit during summer and fall and seek cocooning sites from which they either emerge as second-generation
adults or overwinter as mature larvae until the following
spring. The cocooned larvae can be found in bark crevices on
trees, on props, or in leaf litter and other organic matter on the
orchard floor.
Generalist predators active in the tree canopy, the trunk, or
on the ground may discover and feed on codling moth larvae
in these places. We believe that predation on these codling
moth larvae, either moving to or in cocooning sites, can help
reduce population levels in the following season. However, we
needed real numbers to support our beliefs.
But what is the best way to determine which of the predators we find in orchards are eating codling moth larvae in the
field? Many of these lower canopy and ground-dwelling predators are cryptic in their feeding behaviors. Most predators are
only actively hunting for prey during the night, and they like to
hide in cracks, crevices, ground cover, leaf litter, or soil. Also,
unlike parasitism, it is difficult to find evidence of predation
since usually the whole body of the prey is consumed. Fortunately, new molecular technologies allow us to analyze the gut
content of predators, which gives us a better picture of who is
eating codling moth.
The technique is relatively straightforward, using a primer
in a PCR (polymerase chain reaction) analysis that amplifies
any codling moth DNA that occurs in the gut content of each
predator tested. The tricky part is capturing the predators in
the orchard and collecting them before they have the chance
to fully digest their prey so there is still DNA material available
to analyze.
Dissecting a carabid beetle to remove
gut contents.
Gut content samples after homogenizing with
buffer solution.
Placing gut content of a dissected
carabid beetle into a vial for DNA
analysis.
14
March 15, 2013 GOOD FRUIT GROWER
PHOTOS by ANGELA GADINO, WSU
Pitfall traps
To do this, we used pitfall traps, which are plastic cups sunk
into the soil, where the lip of the cup is level with the ground so
unsuspecting insects will fall into the traps. Since most of
these predators are active at night, the insects or spiders captured in the cups were collected each morning. The samples
were then brought to the laboratory where they were sorted
into groups and frozen until ready for analysis.
The molecular analysis consists of two main parts. First, the
frozen specimens were thawed, sterilized, and placed into
small plastic vials and homogenized with a buffer solution.
For some of the larger species, like ground beetles, the guts
were dissected and used instead of the whole insect body.
The homogenized samples were then ready to undergo
PCR amplification, allowing us to detect codling moth DNA.
Polymerase chain reaction analysis consists of several steps
Preparing gut content samples for spiders, earwigs, and carabid beetles for DNA
analysis.
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